Polyamide resins are generally widely used as engineering plastics having excellent mechanical properties, chemical resistance, oil resistance, gas barrier properties and the like. A polyamide resin obtained by polymerizing m-xylylenediamine and adipic acid (hereinafter sometimes referred to as “MXD6 polyamide”) is widely used because it has higher strength, higher elastic modulus, lower water absorption and better gas barrier properties as compared with polyamide 6 and polyamide 66 and the like so that it can be further coextruded or coinjection-molded with thermoplastic resins such as polyethylene terephthalate, polyamide 6, polyethylene and polypropylene.
However, MXD6 polyamide has high elastic modulus but poor elongation so that films or sheets or the like made from it are too hard to use for applications requiring elongation though they can be used for applications requiring rigidity. It also had the disadvantage that it opacifies/crystallizes and tends to lose transparency during storage in a high humidity atmosphere or upon contact with water or boiling water. No polyamide resin having high elastic modulus and flexibility has hitherto been found.
In patent document 1, the inventors proposed a composition comprising a mixture of MXD6 polyamide with another specific aliphatic polyamide resin having high crystallization speed (e.g., polyamide 6). Films or sheets obtained from this polyamide resin composition are advantageously characterized in that the polyamide resin composition keeps excellent transparency even in a high humidity atmosphere, but disadvantageously showed an increase in water absorption and lower gas barrier properties due to the combination with another polyamide resin as compared with MXD6 polyamide alone. Further, flexibility was insufficient for use in applications requiring softness.
On the other hand, a polyamide resin obtained by polycondensing m-xylylenediamine with sebacic acid (hereinafter sometimes referred to as “MXD10 polyamide”) was proposed and expected for use in such fields as films because the polyamide resin has better elongation properties as compared with MXD6 polyamide. However, the resulting films showed a certain level of elongation but insufficient elongation and further improvements have been required for preparing films, sheets, tubes and the like.